English abstract

This study has included all perinatal deaths in the Croatian health facilities in 2001 and 2002 which met the WHO report criteria, i.e. ≥500g birth weight or ≥22 weeks of gestational age. In order to enhance the quality of perinatal monitoring in Croatia, in addition to mortality rate and level of perinatal mortality and its components, we also require data on the causes of perinatal deaths to make planning of prevention measures possible. Given that risk factors for developing perinatal death can be maternal, infant or common, no one classification of perinatal mortality can fully meet all the specific needs related to monitoring causes of death. Medical practice today mostly uses Wigglesworth pathophysiological classification, Aberdeen obstetric classification and standard International Classification of Diseases and Related Health Problems (ICD), as well as other, less known, classifications. By studying the available literature, no attempt was discovered to combine the two most common perinatal classifications (Wigglesworth and Aberdeen) through ICD codes for the purpose of a more precise determination of underlying causes of perinatal deaths. This aim of this study was to obtain data on the most common causes of perinatal deaths according to the three above listed classifications. The method was connecting Wigglesworth and Aberdeen classification through ICD codes. The purpose was proposing a new classification system to provide more complete information on underlying causes of perinatal deaths. The following hypothesis was formulated: diagnosing maternal diseases/conditions is of greater importance for advancing perinatal care and a favorable perinatal outcome than clinically or pathoanatomically establishing the causes of death in infant. It was assumed that connecting Wigglesworth and Aberdeen classifications through ICD codes could yield more complete information on the underlying causes od death. Before connecting, classification was done according to each of the three classification systems and causes of death were ranked for every component of perinatal mortality. Given that certain causes of perinatal mortality rarely appear in the newborn population, it was necessary to analyze biennial data on the deceased in Croatia. Of 796 deceased, 472 were stillbirths (59.3% of perinatal mortality) and 324 early neonatal deaths (40.7% of perinatal mortality). No significant statistical differences were found in the distribution of the two monitored periods (p=0.377). Kolmogorov-Smirnov test of normal distribution of two components of perinatal mortality for birth weight and gestational age has shown that the obtained distribution for weight and gestation does not follow the Gaussian curve for either variable. According to Mann-Whitney U test, early neonatal deaths were related to statistically significantly lower mean birth weight and gestational age than stillbirths. Mean birth weight in stillbirths was 1935 g, in early neonatal deaths 1691 g. Average gestation duration in stillbirths was 33.4 weeks, in early neonatal deaths 30.9 weeks. The share of stillbirths and early neonatal deaths of low birth weight in overall perinatal mortality was 71.1%, the proportion of premature births before 37th week of gestation 68.7%. By analyzing separately each of the components, the largest share of early neonatal deaths was shown to belong to the 22nd-27th week gestational group (33%), whereas stillbirths were found most numerous in the group with normal pregnancy duration, ≥37 weeks (30.1%). It is a well known fact that the causes of death are closely tied to birth weight and pregnancy duration, and that the incidence of individual causes of death is dependent upon these two variables. According to Wigglesworth classification, the causes of perinatal deaths are divided into five groups: intrauterine, antenatal deaths (45.4%), congenital anomalies (17.2%), conditions related with immaturity (21.7%), asphyxia (7.9%) and specific conditions different from those listed (7.8%). Differences in the distribution of perinatal deaths according to basic groups of causes of death in Wigglesworth classification between two monitored periods are not statistically significant (p=0.594). Each group is further divided into subgroups according to the modified Wigglesworth classification. Leading causes of stillbirth (antenatal and intrapartal) in overall perinatal mortality are the following: antepartal asphyxia (33.3%), antepartal asphyxia with infection (8.7%), other malformations (not classified separately by organ systems; 3.4%), fetal deaths without maceration or known cause (2.6%) and diabetes (1.4%). Leading causes of early neonatal deaths in overall perinatal mortality are as follows: hyaline membrane disease (5.0%), other malformations (4.9%), intrauterine infection (4.5%), hyaline membrane disease with infection (3.6%) and immaturity without details about the cause (2.8%). Only 32.9% of causes from common Wigglesworth groups which contain both stillbirths and neonatal deaths are intercomparable. When displaying causes of death separately for each component, the results show that the leading cause of mortality is asphyxia (83.9% in antepartal deaths and 83.3% intrapartal deaths), whereas in early neonatal deaths the consequences of immaturity (53.5%). Early neonatal deaths due to immaturity have three leading causes: hyaline membrane disease in 23.1% of cases, infection (20.8%) and hyaline membrane disease with infection (16.8%). These most common causes of perinatal deaths are found in two Wigglesworth groups not mutually comparative due to being specific either for stillbirths or early neonatal deaths. Two monitored periods showed no statistically significant differences in the distribution of causes of stillbirth (p=0.176) and early neonatal deaths (p=0.095), which confirms the fact that the period of one year provides enough data on the most common causes of perinatal mortality in Croatia. According to Aberdeen classification, the causes of perinatal mortality are dividied into nine groups: 35.8% of mortality due to maternal disease or other conditions which complicate pregnancy/delivery, 17.2% of mortality due to congenital anomalies, 12.5% due to mechanical causes, most commonly related to umbilical cord complications, 12.3% due to unexplainable reasons, 9.7% due to antepartal hemorrhage, 6.0% due to maternal (pre)eclampsia, 3.1% unclassifiable, 2.6% miscellaneous and 0.8% mortality due to isoimmunization. Differences in the incidence of individual causes between stillbirths and early neonatal births are statistically significant (p<0.001), with greater incidence of all maternal diseases and conditions which complicate pregnancy/delivery in stillbirths, and congenital malformations in early neonatal deaths. According to individual components we find the following: the most common causes of mortality are maternal diseases/conditions during pregnancy in 40.1% of cases, followed by antepartal hemorrhage and mechanical causes (umbilical cord pathology) in 12.1%, accounting for 65% of all causes of stillbirth; the most common causes of mortality in early neonatal deaths are also maternal diseases/conditions during pregnancy (28.7%), followed by congenital malformations (26.5%) and unknown causes (17.9%). Two monitored periods showed no statistically significant differences either in the distribution of perinatal deaths by basic groups of causes of death according to Aberdeen classification (p=0.085), stillbirths (p=0.121) or early neonatal deaths (p=0.061), which confirms that the data collected annually are sufficient to establish the most common causes of perinatal mortality in Croatia. According to ICD, causes of perinatal mortality are divided in two groups: 82.8% of deaths due to certain conditions in the perinatal period and 17.2% of deaths due to congenital anomalies. Each group is further divided into subgroups according to ICD-10 as follows: 60.2% perinatal deaths in certain conditions in the perinatal period group are found in the fetus and newborn affected by maternally related factors and complications in pregnancy and delivery subgroup; respiratory and cardiovascular disorders specific for the perinatal period subgroup accounts for 9.9% of perinatal mortality, whereas the remaining eight subgroups participate in overall perinatal mortality in individual proportions ranging from 0.1 to 3.1%. The distribution of the leading causes of perinatal mortality between stillbirths and early neonatal deaths has demonstrated statistically significant differences in the three leading diagnoses (p<0.001) with substantially higher incidence of chorioamnionitis, placental insufficiency and (pre)eclampsia in stillbirths than in early neonatal deaths. The most common in congenital anomalies group is diaphragmatic hernia from the musculoskeletal anomalies subgroup (20.4%), followed by nervous anomalies and multiple malformations, with an equal share of 18.3%, chromosomal anomalies (13.9%) and circulation anomalies (12.4%). Other malformations are sporadic. Congenital anomalies account for 10.8% of all causes of stillbirths and 26.5% of all causes of early neonatal deaths. Combining the classification systems has yielded significantly more information on the underlying cause of death than the original classifications. By connecting the ICD-10 codes with groups in Wigglesworth classification, it was established that maternal diseases/conditions are the cause of 84% of intrauterine mortality, 66% of mortality due to intrapartal asphyxia and 68% mortality due to immaturity. By combining ICD-10 codes with Aberdeen classification, it was established that maternal diseases/conditions cause 60.1% of all perinatal deaths. The results of this study have shown that the two most frequently applied classification systems in perinatology vary significantly in establishing the causes of perinatal mortality: Wigglesworth classification produces data on immediate, Aberdeen on underlying causes of death. Combining different classification systems has proved the hypothesis that diagnosing maternal diseases/conditions is of greater importance for advancing perinatal care and a favorable perinatal outcome than clinically or pathoanatomically establishing the causes of death in infant. A proposal of a new classification system for determining the causes of perinatal mortality in Croatia is based on the codes of standard medical classification – ICD-10 – with supplements in the form of subgroups taken from Aberdeen and Wigglesworth classifications to provide more information on the most common underlying causes of perinatal mortality, and, in case the underlying causes are unknown, more information on the consequences established in perinatal deaths. Such classification system makes it possible to plan preventive measures in antenatal, intrapartal and postnatal care.